 123 Install Today - GETTING CLOSER..., PROGRESS: BAD MPS |
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| technicalninja |
 Apr 28 2024, 10:00 AM
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#101
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Senior Member  Group: Members Posts: 1,827 Joined: 31-January 23 From: Granbury Texas Member No.: 27,135 Region Association: Southwest Region 
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Started another thread regarding possible backfire protection of the MPS.
Didn't want to clutter up your thread. Rick http://www.914world.com/bbs2/index.php?showtopic=370118 |
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| FlacaProductions |
Apr 28 2024, 02:05 PM
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#102
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Senior Member Group: Members Posts: 1,733 Joined: 24-November 17 From: LA Member No.: 21,628 Region Association: Southern California
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I appreciate that - and I'll test the "old" one asap to confirm but it has clearly been opened whereas the new one is the correct model and has not been opened.
The difference as been night and day. Just went for two quick rides and the head temps stayed in check (floating around 350ish depending on load, etc) and oil was at 210. |
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| FlacaProductions |
Apr 29 2024, 07:48 AM
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#103
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Senior Member Group: Members Posts: 1,733 Joined: 24-November 17 From: LA Member No.: 21,628 Region Association: Southern California
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Update on my MPS testing: holds 15lbs of vac for 30 mins - so that checks out - and I got 95 ohms across 7 and 15 and 345 ohms across 8 and 10. So that checks out.
But the fact remains that swapping in the "new" one and it runs great. |
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| Superhawk996 |
Apr 29 2024, 08:43 AM
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#104
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914 Guru Group: Members Posts: 6,469 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch
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QUOTE(FlacaProductions @ Apr 29 2024, 09:48 AM)  Update on my MPS testing: holds 15lbs of vac for 30 mins - so that checks out - and I got 95 ohms across 7 and 15 and 345 ohms across 8 and 10. So that checks out. But the fact remains that swapping in the "new" one and it runs great. I’m going to put this post from the other thread here. This pretty much mirrors your situation where it holds vacuum but doesn’t respond properly. Long ago when working on friends car, I used to run into the situation where a MPS wouldn’t work and we simply swapped them back when parts were plentiful (late 80s - early 90s). This was long before the availability of replacement diaphragms and affordable LCR testers. Let us know what you find when you get around to MPS tear down. QUOTE(ChrisFoley @ Apr 28 2024, 05:28 PM) QUOTE(Superhawk996 @ Apr 28 2024, 11:33 AM) That metal diaphragm isn’t terribly sensitive to backfire but I have no doubt that if you have one that’s already fatigued and has a hair line crack (but holding vacuum), a backfire could finish it off and crack it. ^^^ This I've rebuilt many units which held vacuum ok but didn't perform well in use. The diaphragm was always cracked already when I disassembled them. The diaphragm is under spring pressure when the engine is not running and while at WOT. The perimeter support surface has a sharp corner that creates the fatigue which eventually cracks the diaphragm. A sudden transition to positive pressure could be the last straw. |
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